This argument allows you to specify the server to connect to; see X(7)
.

-screen screen

When multiple displays are configured as a single logical
display, this option allows you to select the screen you wish to change.

-quiet

Silence the normal output of xgamma

-help

Print out the `Usage:' command
syntax summary.

-gamma f.f

The gamma correction can either be defined as a
single value, or separately for the red, green and blue components. This
argument specifies the gamma correction as a single value. If no value for
the gamma correction is given xgamma returns the current gamma correction
of the display.